Acrylic and methacrylic acids are the simplest unsaturated organic acids. Due to the presence of unsaturated carbon-carbon double bonds, these acids readily react with electrophilic, free radical and nucleophilic agents. Free radical-initiated polymerization of the double bonds is the most common reaction. Minor amounts of the acids are normally used as comonomers to vary the mechanical properties of other polymers. Most of the acrylic and methacrylic acids are used in the form of their ethyl, methyl and butyl esters.
The polymerized acids themselves are brittle solids that cannot be molded and therefore their use is very limited. It is also known that these polyacids are easily dehydrated to form polyanhydrides. Generally, the glass transition temperature (Tg) of the dehydrated polyacids increases with an increase in anhydride concentration.
Although not of commercial importance, acrylic and methacrylic anhydrides can polymerize to form polyacrylic and polymethacrylic anhydrides. The mechanical properties of the polymerized polyacids and polymerized polyanhydrides have not been reported in the literature.
Grafting of vinyl monomers onto an olefin polymer backbone is disclosed in U.S. Pat. No. 5,140,074, where graft copolymers are made by contacting an olefin polymer with a free radical polymerization initiator, such as an organic peroxide, and a vinyl monomer in a nonoxidizing environment, deactivating residual free radicals, and decomposing unreacted initiator. Acrylic and methacrylic acids are described as suitable vinyl monomers. U.S. Pat. No. 5,411,994 discloses a process for making graft copolymers by irradiating an olefin polymer and then treating with a vinyl monomer in liquid form in a nonoxidizing environment, deactivating free radicals, and removing unreacted monomer.
It has been reported in the literature that incorporation of ionic moieties such as methacrylic acid into polystyrene raises the Tg significantly (.about.3.degree. F./mole % of methacrylic acid). We have found an improvement in the heat resistance of polypropylene graft polymerized with styrene and methacrylic acid to form styrene/methacrylic acid copolymer side chains. However, when the methacrylic acid is incorporated into the polymer chain at levels up to 40 mole % there is a corresponding reduction in the ductility of the product as indicated by weldline strength, elongation, and difficulty in impact modification and extrusion
There is no known process for making graft copolymers containing anhydride groups from a propylene polymer material having graft polymerized thereto acrylic acids substituted with 1-3 C alkyl groups. Thus, the effect such anhydride groups would have on the mechanical properties of the graft copolymer product is also unknown.